ISCET Digital Electronics Principles 3

Question 1

In two's complement representation using 8 bits, what is the decimal value of 11110000₂?

Accepted Answer

-16

Answer

11110000₂ in two's complement: invert to 00001111 (15) then add 1 = 16, so the value is −16.

Question 2

Which type of counter produces a modulus that is not a power of two by using feedback to skip states?

Accepted Answer

Modulo-N counter

Answer

A modulo-N counter uses decode-and-reset or feedback logic to count to N−1 then recycle, regardless of whether N is a power of two.

Question 3

What is the primary purpose of a tri-state buffer in a digital bus system?

Accepted Answer

Allow multiple devices to share one bus line without conflict

Answer

A tri-state buffer can be disabled to a high-impedance state, letting multiple drivers share a bus without logic conflicts.

Question 4

Apply De Morgan's theorem to simplify (A·B)':

Accepted Answer

A'+B'

Answer

De Morgan's theorem states (A·B)' = A' + B': the complement of a product is the sum of the complements.

Question 5

Which flip-flop condition is considered FORBIDDEN in an S-R (Set-Reset) latch?

Accepted Answer

S=1, R=1

Answer

When both S=1 and R=1, the latch enters an indeterminate state because both outputs try to be active simultaneously.

(ISCET) International Society of Certified Electronics Technicians Practice Test